1. Field of the Invention
The invention relates to the field of containers for providing liquid concentrates for making ready-to-use dialysis fluid for a dialysis treatment of a patient by an artificial kidney.
2. Description of the Related Art
In case of kidney failure the functions of the human kidneys have to be substituted by an artificial kidney device. Wide spread therapies comprise peritoneal dialysis and hemodialysis. In peritoneal dialysis, dialysis fluid is conducted via special implanted catheters to the peritoneal cavity of a patient and regularly exchanged with fresh fluid, thus purifying the human blood by diffusion of substances to be removed and by extracting excess water by osmotic pressure gradients through the peritoneum of the patient.
In hemodialysis the blood of a patient is circulated in an extracorporeal blood circuit for several hours. The blood passes the blood chamber of a dialyser where a semipermeable membrane, most commonly in the shape of thousands of hollow fibres, separates a blood chamber from a dialysate chamber that is part of a dialysate circuit. The blood is purified from substances to be removed by diffusion through the membrane as such substances are 20 usually not contained in the dialysate flowing into the dialysate chamber. Other substances that are to be retained in the blood at least in certain concentrations and that can also pass the membranes like electrolytes are contained in the fresh dialysate in physiological concentrations. By applying a pressure gradient excess water can be transferred from the blood to the dialysate chamber and then be removed together with the dialysate exciting the dialysate chamber.
Most contemporary hemodialysis devices prepare the dialysate required for the hemodialysis treatment during the treatment from concentrates and water in a single-pass system, i.e. the prepared dialysate only passes the dialyser once and is discarded thereafter. Depending on the type of dialysate to be used one or two concentrates are required. In the case of bicarbonate dialysis that currently represents the most common dialysis mode two concentrates are necessary because of chemical incompatibilities of some of the substances. The first or “A”-component usually consists of an acidic part that also contains most of the required electrolytes. The second or “B”-component consists mainly of sodium bicarbonate in this case. Whereas the second component can also be delivered in dry powder form, the first component is still widely distributed as a fluid in rigid containers if no central concentrate supply system exists where the concentrate is prepared at a central location and then distributed to the treatment places via a piping network.
Typical dilution ratios of the A-component with water are about 1+33, 1+34 or 1+44, the B-component contributing further shares between 1 to 2 parts of liquid. Common dialysate flow rates for a hemodialysis treatment are of the order of 500 mllmin. Taking a four hour treatment a liquid volume of about 120 liters has to be circulated through the dialysate chamber requiring concentrate volumes of at least 3 to 4 liters each. To enable a variation of concentration ratios and also to provide a certain tolerance to prolong a treatment and to compensate the waste of dialysate in certain conditions of a hemodialysis device when for security reasons the continuously prepared dialysate is short-circuited to the drain, usual containers for liquid dialysate concentrates contain 5 or more liters of liquid concentrate.
The dialysate prepared by diluting the concentrates with water on-line during a treatment of a patient may also be used as substitution liquid in the case of a hemofiltration or hemodiafiltration treatment. Today many treatment devices also provide for such on-line substitution modes leading to an even higher demand of liquid concentrates.
Up to now the fluid concentrates have usually been delivered in rigid plastic containers as the weight of the concentrate requires a certain stability of the container. Such containers also simplify the shipping of large lots as they can easily be arranged in layers on top of each other.
These rigid containers have the disadvantage that because of their rigidity they are comparatively expensive as the container walls have to be thick enough leading to higher material expenses. Furthermore, the empty containers are bulky making the further processing cumbersome. The large amount of material to be recycled or discarded adds further to the cost.
It is an object of the present invention to provide a container with liquid dialysate that requires less material in the manufacturing process but still provides sufficient stability to the filled container even when being filled with three liters of liquid and more and during the use of the container when the container is gradually emptied.
The problem of the invention is solved by a container filled with a liquid dialysate for making dialysate for a dialysis treatment, characterised in that the container is a self-standing bag made of flexible elastomeric sheets.
The invention is based on the observation that in other technical fields self-standing bags made of flexible elastomeric sheets are in wide-spread use. Such bags require much less material for their production and much less space when being empty. However, there appeared to be the prejudice in the field of dialysis that such bags are not suitable for the manufacture of containers for liquid concentrates for dialysis. In fact the weight of several kilograrnms of liquid is large for a flexible bag bearing the risk that a bag may crack during use or not rest in a stable position to allow the extraction of the concentrate through the suction pipe of the hemodialysis device during a treatment procedure.
In the framework of this patent application a self-standing bag is understood to be a bag having its barycentre well defined above its bottom standing area when being filled with a medium so that the filled bag rests in a stable standing orientation on its own.
The inventors of the present invention observed that this prejudice can in fact be overcome and that it is possible to produce self-standing bags made of flexible elastomeric sheets filled with liquid dialysate concentrate having a volume of three liters and even more.
In a preferred embodiment this bag is made from two elastomeric flexible side wall sheets having rectangular shape with horizontal top and bottom and two vertical edges, and one elastomeric flexible bottom wall sheet also having rectangular shape with two horizontal and two vertical edges. When being empty this bag may be put into a flat configuration where the bottom wall sheet is sandwiched between the two elastomeric side wall sheets and wherein the bottom wall sheet is symmetrically single-folded parallel to its horizontal edges and the horizontal edges of the bottom wall sheet coincide with the horizontal bottom edges of the two side wall sheets. In the flat configuration the empty bag is thus divided into a lateral four-layer part in the lower part of the bag and a lateral two-layer part in the upper part of the bag.
A connector part can conveniently be sandwiched between the two horizontal top edges of the side wall sheets wherein the two horizontal top edges and the connector part are joined in a fluid tight way by a seal, preferably a welding line.
In further embodiments of the invention several parts of the bag are jointly sealed, preferably by welding: the vertical edges of the side wall sheets in the lateral two-layer part, the vertical edges of the bottom wall sheet with the neighbouring parts of the side wall sheets, and the horizontal edges of the bottom wall sheet with the neighbouring horizontal bottom edges of the side wall sheets.
A preferred embodiment of the bag comprises first sloped sealing lines on each side of the bag joining the side wall sheets in the lateral two-layer part between first points on the horizontal top edges of the side wall sheets that are recessed from the outer ends of the horizontal edges, in other words, the first points on the horizontal top edges of the side wall sheets are spaced from the vertical edges of the side wall sheets, and second points that are along or spaced from the vertical edges of the side wall sheets and that are positioned on the line separating the lateral two-layer part from the lateral four-layer part. Second sloped sealing lines join each side wall sheet and the neighbouring bottom wall sheet in the lateral four-layer part on each side of the bag between third points on the horizontal bottom edges that are recessed from the outer ends of the horizontal edges, in other words, the third points are spaced from the vertical edges of the side wall sheets, and the second points.
The second points may be recessed from the vertical edges of the side wall sheets and the bag may comprise further horizontal sealing lines between the second points and the neighbouring vertical edges of the side wall sheets along the line separating the two-layer part from the four-layer part thus joining all four layers along these horizontal sealing lines.
In a particularly stable embodiment of the self-standing bag there are third sloped sealing lines on each side of the bag between the third points and fourth points on the vertical edges of both the side wall sheets and the bottom wall sheet in the four-layer part joining only the bottom wall sheet and the neighbouring side wall sheet. Additional fourth sloped sealing lines on each side of the bag between the second and the fourth points joining only the bottom wall sheet and the neighbouring side wall sheet further contribute to the stability of the self-standing bag.
In another embodiment of the invention the first, second and fourth sloped sealing lines, but not the third sloped sealing lines exist. Instead the sheet material of the side wall sheets and the bottom wall sheet in the corner areas below the second sloped sealing lines and below cutting edges leading from the fourth points to fifth points on the second sloped sealing lines is removed. The cutting edges may be reinforced by fifth sloped sealing lines on each side of the bag between the fourth and the fifth points joining only the bottom wall sheet (4) and the neighbouring side wall sheet. In this case a beak-like flap is formed on both sides of the bag that protects the zone around the second points where four sheets of the side wall sheets and the bottom wall sheet are joined.
All sealing lines are preferably created by welding techniques, but generally other joining processes like gluing are also possible. In special cases a sealing line may simply be established by folding a larger sheet along the required line. Such embodiments are hereby explicitly encompassed by using the expression “seal” throughout this document. Furthermore, the sealing lines are preferably straight lines.
In a particularly preferred embodiment of the self-standing bag the sheet material of the bottom wall sheet between the fourth sloped sealing lines and the vertical edges has been removing, preferably by punching. Both side wall sheets can therefore directly be joined in this area thus avoiding welding areas consisting of four layers of elastomeric sheets that could give rise to problems in reliable sealing the outer layers.
The second sloped sealing line may at least partly be a peel seam that is adapted to absorb excessive pressure in the bag. Should high pressure suddenly develop in the bag as in the case of a crash of the bag on a hard floor the peel seam can at least partly open whereby the pressure is diminished in a controlled manner minimising the risk that the bag gets cracks.
With the self-standing bag according to the invention it is possible to provide dialysate liquid concentrates in a bag made of elastomeric flexible sheets with common volumes of 3 to 8 liters, preferably 5 to 6 liters. Such a bag could also be delivered containing just a dry or slurry concentrate that when being diluted with water directly before use produces the same amount of dialysate liquid concentrate that is sufficient for a whole blood treatment of a patient.
For embodiments of the self-standing bag according to the invention where the bag is made from two side wall and one bottom wall sheets a further advantageous embodiment makes use of a layered bottom wall sheet wherein the two outer layers consist of different materials. Using the same material for one outer layer of the bottom wall sheet and the side wall sheets or at least the outer layer of the side wall sheets facing each other further simplifies the manufacture of certain embodiments of the self-standing bag according to the invention as the stability of a bag area where four sheets would have to be joined by welding can be enhanced without the removal of parts of the bottom wall sheet.